1. Field of the Invention
The present invention relates to an apparatus for chamfering through press forming edges of a rim element provided on a disk wheel manufacture line.
2. Description of the Background Art
On a conventional disk wheel manufacture line for manufacturing disk wheels for a vehicle, disk wheels are manufactured in the following way. At first, a flat steel plate for a rim element is rounded by a coiling machine into a rounded plate and both circumferential end portions of the rounded plate are pressed to form flat portions so that the end portions can be butt at the flat portions. Then, the flat end portions of the rounded plate are butt and welded to form a cylindrical rim element which has a flat portion at the welded portion. The welded portion is trimmed. Then, both axial end portions of the cylindrical rim element are pressed in the axial direction thereof and are flared using a flaring machine so that a rim shape is produced including rim bead seats and flanges. In addition, the cross section of the cylindrical rim element is shaped into a true circle. After flaring, the edges of the cylindrical rim element are chamfered through press forming by imposing an axial force on the flared cylindrical rim element. Then, the rim element is welded together with a disk element to form a disk wheel. Finally, the disk wheel is painted.
The reason why the edges of the rim should be chamfered is to prevent a worker from being injured by the sharp edges during manual handling in the manufacture, to prevent the paint from peeled off the edges of the rim, and to improve an outside view of the rim portion of the disk wheel.
However, in the prior art, since chamfering of the edges of the rim element through press forming is performed after flaring and such flared rim element has a small axial rigidity, the rim tends to be easily deformed when it receives a large axial force during press forming. The reason why the chamfering has been performed after flaring in the prior art is that the rim element to be chamfered does not have a generally true circle cross section because of its flat portion which has been thought to be inevitable for butt-welding. In addition, chamfering through press forming accompanied by rotation of the rim element can not be applied to a cylindrical element which does not have a generally true circular cross section. A chamfering through machining of the edges of the rim element having no generally true circle cross section may be possible without imposing a large axial force on the cylindrical element, but such chamfering through machining will increase cost and time of the manufacture and is not practical.
However, the inventors have found that chamfering through press forming can be performed before flaring by developing a butt welding method or an apparatus in which the end portions of a rounded plate are left rounded without providing flat portions therein and are butt welded. For example, a circumferential force may be imposed on the end portions of the rounded plate. The apparatus in accordance with the present invention is applied for chamfering the edges of the rim element having a generally true circular cross section.